This study is based on two challenges: (1) The need to develop an effective system for tumor delivery of poorly-soluble anti-cancer drugs, and (2) The need to achieve enhanced drug delivery into tumor cells in response to local tumoral stimuli. We have chosen paclitaxel (PTX) as a poorly soluble drug and extracellular matrix metalloprotease 2 (MMP2) that is up-regulated in many tumors as a local tumor stimulus, to which a drug delivery system for PTX should react. An easy-to-prepare self-assembling micellar system was chosen as a general platform in this research. We have designed a novel amphiphilic polyethylene glycol (PEG) 2000-PTX conjugate where PEG and PTX are conjugated via a MMP2-sensitive peptide (PEG2000- peptide-PTX, pro-drug), which can self-assemble into a core-shell structure and respond to up-regulated MMP2, resulting in tumor-specific drug release. This conjugate with two other amphiphilic conjugates - PEG1000-phosphatidyl ethanolamine (PEG1000-PE) for additional micelle stabilization and TATp-PEG1000- PE to add a cell-penetrating function - self-assembles into mixed micelles, where drug and TATp are shielded by the longer PEG2000 chains when en route to a tumor, but become exposed after MMP2-mediated detachment of the PEG2000 blocks in the tumor and allow for enhanced intracellular delivery of the active drug. Such a preparation ensures: (i) higher PTX loading efficiency, (ii) low premature PTX release, (iii) blood longevity and better tumor accumulation via the enhanced permeability and retention (EPR) effect, and (iv) enhanced drug internalization by tumor cells due to the presence of TATp moieties, which become exposed inside the tumor after the MMP2 action. Using this micellar system, promising in vitro and early in vivo data have been obtained in terms of its tumor cell-specificity and cytotoxicity. We hypothesize that this novel MMP2-sensitive system will significantly improve the delivery of the drug into tumor cells, resulting in an enhanced antitumor effect and decreased off-target toxicity. The following specific aims will be pursued to test this hypothesis: (1) To prepare and optimize the MMP2- responsive paclitaxel(PTX)-loaded self-assembly micellar nanoparticles using TATp-PEG1000-DOPE; PEG1000-PE; and MMP2-sensitive PEG2000-peptide-PTX (pro-drug) building blocks; (2) To investigate cellular uptake and cytotoxicity of PTX-containing, MMP2-sensitive nanopreparation in vitro using A549 human non-small cell lung cancer and HT-1080 human fibrosarcoma cell lines with up-regulated extracellular matrix MMP2; (3) To perform experimental tumor therapy in vivo in mice using a cancer cell line selected after Aim 2 based on the highest response (maximum level of cell killing) to the MMP2-sensitive nanopreparation. This study will introduce a novel type of stimuli-sensitive preparations of poorly-soluble anticancer drugs with increased efficacy, and become the basis for the subsequent R01 proposal to show the applicability of the approach for other poorly-soluble drugs and the broad variety of tumors with up-regulated MMP2.